A zoom lens having a four-lens-group configuration of positive-negative-positive-positive has been known (for example, see Japanese Patent Application Laid-Open No. 1-352400). The positive-negative-positive-positive four-lens-group type zoom lens is composed of four lens groups which are, in order from an object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power. Upon zooming from a wide-angle end state, which gives the shortest focal length, to a telephoto end state, which gives the longest focal length, at least the first lens group and the third lens group move toward the object side. Moreover, in a digital still camera and a video camera using a solid state imaging device, according to recent increase in integration of photodetector element, an area of each photodetector element becomes smaller, so that an optical system has been required to be faster and high optical performance at the same time. Moreover, as a matter of photographing convenience, a digital still camera having a high zoom ratio and excellent portability has been required.
However, in an imaging device having large number of pixels, a conventional optical system cannot obtain sufficient optical performance over large photographing area, and tends to become large because of a large aperture. As the optical system becomes large, portability becomes worse. Moreover, in order to increase possibility of photographing expression of an photographer, a zoom lens having a wide angle of view has been requested. With using a wider angle of view, it becomes possible to enjoy photograph with high flexibility. However, a high zoom ratio, a wider angle of view and high optical performance are very hard to compatible. Even if they are compatible, the optical system becomes large.